Veteran actor Helgenberger, who plays blood spatter analyst Catherine Willows on the hit show, spilled the beans during a French radio interview -- but it wasn't all diss. She says that while Bieber was a total brat, he wasn't a totally bad actor.

"Justin Bieber wasn't bad," Helgenberger said. "He had never acted before. I shouldn't be saying this, but he's kind of a brat. He was actually very nice to me, but he locked one of the producers in the closet. And he put his fist through a cake that was on the table."

"I am pretty open to whoever comes on the show," Helgenberger continued. "If someone is a jerk, that bothers me. If they're a so-so actor, it doesn't bother me. [Bieber] is actually better than you'd think!"